Broken document

[Jürgen Spitzmüller]

Am Mittwoch, dem 15.03.2023 um 16:54 +0200 schrieb Udicoudco:
> You get the error because you load amsmath (it is loaded via
> newtxmath) before refstyle. See the attached .tex file which produces
> the same error.  If you will load newtxmath via Document->Settings-
> >Latex Preamble and set the Math Font in Document->Settings->Fonts-
> >Math to automatic, there will be no error (see the attached LyX
> file)

Note that this only covers the problem (and potentially causes others).
The real problem is in refstyle.cfg which is incompatible with recent
AMS maths due to the robustification of commands such as \eqref.

See https://tex.stackexchange.com/questions/675145

Seems like the refstyle author has been made aware of the problem, but
it is unknown whether he is still willing to take care of the package.

If no solution on the package side appears on the horizon, a workaround
in LyX would be to add

\DeclareRobustCommand\eqref{\relax}
\let\eqref\relax

before refstyle is being loaded (this would need to be done in the LyX
code and with package version check, and it is really something we'd
like to avoid as it basically disables refstyle's support for AMS math.

-- 
Jürgen